1. Field of the Invention
The present invention relates to a rotary pump with better fluid sealing structure and a brake apparatus having the same. In particular, the present invention is preferably applied to an internal gear pump such as a trochoid pump or the like for brake apparatus for vehicles.
2. Description of Related Art
A rotary pump, for example, an internal gear pump, is comprised of a drive shaft to be driven by a motor, an inner rotor and an outer rotor to be rotated by the drive shaft and a casing for containing the drive shaft and the inner and outer rotors. The inner and outer rotors contained in the casing form a plurality of teeth gap portions constituted by inner teeth portions of the outer rotor and outer teeth portions of the inner rotor which are in mesh with each other. An intake port and a discharge port are disposed on opposite sides of a pump center line passing through the respective rotation axes of the inner and outer rotors.
When the drive shaft is rotated for driving the pump, the inner rotor is rotated with the drive shaft with an axis of the drive shaft and, according to the rotation of the inner rotor, the outer rotor is rotated in a same direction as the inner teeth portions of the outer rotor are in mesh with the outer teeth portions of the inner rotor. As the respective volumes of the teeth gap portions between the inner and outer teeth portions are varied in every turn of the rotating inner and outer rotors, fluid is sucked from the intake port and discharged to the discharge port.
In the pump mentioned above, there is a problem that the fluid is likely to leak from a high pressure side to a low pressure side through various clearances or gaps in the casing, since fluid pressure at the discharge port (hereinafter called discharge pressure) is higher than fluid pressure at the intake port (hereinafter called intake pressure) when the pump is driven.
In more details, the high pressure fluid at the discharge port leaks to the low pressure intake port or a clearance between the drive shaft and the inner rotor through clearances between the casing and axial end surfaces of the inner and outer rotors, to the low pressure intake port through a clearance between the casing and an outer circumference of the outer rotor or to the low pressure intake port through teeth top gaps formed by forcing the meshed inner and outer teeth portions open.
To cope with these problems, it is possible to narrow the clearance between the casing and the axial end surfaces of the inner and outer rotors or to diminish the clearance to such an extent that the casing and the axial end surfaces of the inner and outer rotors are always in direct contact with each other. However, even if the clearance is narrower, it is very difficult to prevent the fluid leakage and the extremely diminished clearance causes a mechanical loss due to the increased contact resistance with the casing.
Further, it has been proposed to arrange a sealing member between the casing and all of the axial end surfaces of the rotors to restrain the fluid leakage. This is also likely to cause a mechanical loss due to the larger contact resistance with the sealing member.
Furthermore, to prevent the fluid leakage from the outer circumference of the outer rotor, it has been proposed to arrange sealing member in recessed portions provided at an inner wall of the casing that faces the outer circumference of the outer rotor. However, it is very difficult to provide the thickness of the sealing member (the thickness in an axial direction of the inner and outer rotors) always equal to that of the casing because of manufacturing dimensional errors of the sealing member on the molding or machining processes thereof. If there exists a clearance between the casing and the sealing member due to the dimensional errors, fluid leaks through the clearance.